Finishing leather



Patented Jan. 9 1940 UN E "STATES.

' Fredrick J. Wallace, Erie, rs; assignor t6 Robeson I Process Company, NewYork, Y., acorpora; j

I tion or New Jersey,

I No Drawing. .Applicatlbn July f1z, i 938, I Serial No. 218,831 1 (onus-'4) s This invention or discovery relates'toflnishing leather; and it comprises a method of finishing partially ftanned leather wherein there is incorporated in the leather a substantial amount of lignin recovered from liquors produced by the digestion of wood with alkaline liquids; and it comprises as 'a new material linished'leather containing substantial amounts otyrecoveredlignin; all as more fully'hereinaiter'set forthand as claimed. 1 m s Lignin is a group name for the non-cellulose components of woody fiber. In the acid processes of making paper pulp it reappears in the form of soluble sulionic acid salts andacids; as ligno sulfonates which contain sulfur, as the sulionic group, as an essential constituent. In the alkaline processes of making pulp, the caustic soda process and the sulfate process, it reappears in solution in the black-liquor withdrawn from the cellulose. This liquor contain'slignin as such although the lignin is probably not in a state in which it exists in the wood where it is-in combination with cellulose as lignocellulos'e. This somum is quite impure and ordinarily contains .geous for use in the present invention.

, leather is'generally produced by a series or treat- In producing leather, the'hides and skins are customarily treated with an infusion of tanning materials or tanning-liquors and various procedures are used to obtain the desired'degree of tannage. For instance, vegetable tanned sole ments with tanning liquors of various strengths;

the strength of .the' tanning liquors contacted with the hide being gradually increased to a maximum and then gradually decreased in successive j 1 steps.

In an ordinary procedure the first stage .of' tanningis produced by rocking the hides in tanning liquors. the strength ofgwhich is gradually increased. The partially tanned hides coming ffrom the rocker yard are then laid, away in pits containing tanning liquors of higher concentra-,

tion, these pits being knownas layers" and the line lignin solution thereto. ,This may be doneat any stage after the fhide'hasbeen partially tanned, for instance; after the'rocking of the hide. and, the natural acids, present in. the hide water containing caushide being treated successively in severallayers to efiect this next stage in"the'ta'nnlng procedure. After removaljrom the last layer, generally the hides are drummed in aconoentrated solution oi atanning agent to complete the tan- 6 ning. These drums are known ase'irtract wheels, and this treatment with concentrated tanning liquors, that is, strong liquors, isknow'n as drummingor extracting) Tanning liquors-are generally known as extracts and this procedure puts extract into the-hide. After removal from-the extract wheel, the [tanned hides are tempered by immersing them in vats containing'weaker tanvvningliquids or solutions." After'r'ern'oval from the last tempering vat, the hides may be wrung, bleached, oiledand dry-'dipped'prior tofinishing. In-ali stages of the vegetablev tanning process, the tanning solutions are of acid character and the tannedhide has a substantially acid reaction, h p ns f onifi-oi 2- I have discovered that an increased'degree of tannage and. other betterments areobtained by incorporating in the tanned hides a substantial amount of lignin as by ap lying a nightly alkahide in tanning" liquors. The slightlyalkaline solution of lignin penetrate'sand impregnates the graduallyjneutrali ze the slight alkalinity ofthis solution, :thus precipitating the lignin in the hide in insoluble form. addition can be made at any "or the stages usually employed in tanning. That is, this'lncorporatlon of 'the lignin may be effected as'part of the tanning procedure and I obtainimprov'ed-leathers irrespective of the particular'stage at which the lignin is incorporated. The sojtreated'hides, after the usual operations are completed, yield leathers; showing an increased degree of tannage and other improved qualities. V

1 floweven advantageouslythe lignin may be incorporated during the extracting or drumming operation, that is, the tanned hides from the last layer may be drummed with alkaline lignin solutions-having. apH of approximately v8.2 to 9.2. Such a. solution readily penetrates and homo- =geneously impregnates the moist partially tannedf hideg-during the drumming, Drumming in the extract-wheel is continued until the weakly ion-' ized or dissociated natural acids present in the wet hide completely precipitate all of the'lignin in insoluble form. Likewise, the lignin may be incorporated in the hide as part of the other 0pmay be employed trations of my methods trolled to, produce tageous. The tanning with the usual tanning. agent havingbeen completed, the treatment with the slightly alkaline lignin solution can be conleathers meeting particular specifications as to degree of tannage and other qualities. In this way leathers having the desired qualities may be reproduced irrespective of variations in the hides and tanning agents em- I p ow d In some casesthe precipitated washed lignin v in tanning operations direct, but as a ruleI'iind it betterto dissolve it in al preparing lowingprocedure is advantageous: The black liquor is treated with sufllcient acid to neutralize the alkalinity and to precipitate the lignin. .Any

acid may be used. Alter separating the acid mother liquor, the precipitate is washed with water until free of soluble material. The wet precipitate is then dried or dehydrated to remove excess moisture. It may be ground to a powder if desired. So prepared, this lignin is sufllciently tree or deleterious materials to be useful in tanning.

For precipitating the lignin I usually employ sulfuric acid, but other suitable mineral or inorganic acids may be employed. The acid'treatment of the black liquor in addition to precipitating the lignin also forms volatile sulfides and mercaptan compounds, when some types of black liquors are employed. Volatile and soluble materials are removed during the washing and drying. The following examples are typical illusof recovering lignin useful for my purposes from two types of commercial black liquors.

Example 1.--This example illustrates I the rerecoveryof lignin from a spentblack'llquor ob- .tained as a byproduct in treating wood by the krait process; the liquor having a solid content of 19.10 percent and a free alkalinity of 2.10'per cent calculated as NaOH.

To 10,000 pounds of liquor'were added, with stirring, a solution of 380 pounds of sulfuric acid in an equal amount of water. This acid treatment in this case develops volatile sulfides and mercaptan compounds and precipitates lignin as a brown flocculent material. After the mixture has been thoroughly stirred, .it is allowed to settle for two hours- Then the mixture is heated to 160 F. toflocculate and coagulate any lignin remaining suspended in the mother liquor. This heating also drives of! some of the volatile sulfides and mercaptans. The mother liquor'is then decanted from the lignin which has settled out.

The separated lignin is washed with water, driedand ground to a powder. "The washing andjdryingremove water-soluble bodies and volatile materials. In this'way approximately '870 pounds or. purified lignin are obtained.

Similarlignin preparations useful for the present purposes may be also obtained from the black lignin from black liquor the folliquors resulting from the soda process. This is illustrated in the following example:

Example 2.In this example, a soda process black liquor having a free alkalinity of 2.90 per cent and total solids of 22.29 per cent is employed.

To 10,000 pounds of such black liquor there is added 500 pounds of sulfuric acid dissolved in 500 pounds of water. "The ligrnnisprecipitated as a reddish-brown flocculent material. The mixture is agitated for 2 hours and then heated to 160 F.

' to flocculate and coagulate the precipitated lignin. The lignin isthen filtered from the acid 'mother liquor, thoroughly washed with water and dried. In this way, approximately 810 pounds 01 I dry material is obtained.

The dry lignin preparation obtained in the above examples may be'converted into alkaline lignin solutions suitable for treating leather, by suspending the lignin powder in water and then adding just sufllcient caustic soda to this suspension to dissolve the lignin. The resulting solutions have a pH value slightly on the alkaline side. Those having a pI-Ivalue between 8 and'9.2. are advantageous for the present purposes. These solutions can be used as they are intreating leather, or they can be evaporated to a greater concentration. By evaporating to dryness I obtain dry slightly alkaline lignin preparations which are used in treating. wet hides, in some modifications of the present invention.

. The following examples illustrate the manufacture oi these preparations:

Example 3.-This example illustrates the preparation of an alkaline, lignin solution suitable for dry dipp s- In 1760 pounds or water there is suspended 870 pounds or the lignin powder obtained in Example 1. This mixture is agitated and 52 pounds of sodium hydroxide are added, and the stirring continued until a uniformsolution of lignin is;

eter, a solution advantageous for dry dipping is obtained.

Example 4.-This example illustrates my naethods in improving leather by dry dipping.

The lignin solution of 60 barkometer obtained by Example 3 is heated to 110' r. and rough dried vegetable tanned leather immersed in this ao'lution. The temperature is maintained'untilthe lignin isprecipitated in the leather. Approxi- I mately one hour is required.

Then the leather is removed and further treated and untreated leathers:

Leather before Leatherette:

dry dipping in dry dipping in alkaline lignin alkaline lignin Insoluble ash -1 o9 .os 11. 42 ll. 11

Water soluble..." 15. 02 11.83 Combined tannin 20. 38 36. 31 Total 100.00. 100.00 Degree tonnage"... 71. 2 95. 8 g}! 3. 03 4. 09 moral acidity... 1.40 .00

Thereafter the so treated i .From the aboveanalysisthe increasedilegree of tann'age and otherinnprovementsobtained i hy sc incorporating :the@lignin ginto the eathen are cvii limit--3 iignin recovered51mmsodaprccessliil'luor.; 4 a

. 810 pounds ofathe,.;dry lienin5powderiq te il diiil JEXamDIeHZ. nllhis mixture isifagitated and 40w v f pounds'of sodiuniihydroxide areadded;

tation 'is'continued :11I1ti1 8|a'11 nif01fmsolution lignin .:is"=obtai,ned.- I resuitihiaolutiim' 'pH value 01' 9.0 :and contains appro'ximatel 3;

per. 'centby weight .of solubilized 1 r'I'his:solutic'vmmay beus'edtoatl mtga-11d .131938 :natezl eatherasdescribed: inxExample.

may-b amedobmmmugnuyan'f len t .1 powder whichdsvalsouceiulioraddition to tanned :iThis vegetable; tanned; leather.,; ,is ch the usual; oil twheelvandethen; the alkaline lignin ".01 :dry .leather.. After .the powder has Combined tannin.

1 powder. described.in;ExamD1 is-lintroducedjimq unds the .drumlin 11a 'ratioof 12- no name The iollowinetable- IiVesj-thef analysis -roi the treatediandiuntreatedi leathers: v

' Leatherbcim drum ing withai alino lignin Inlolublouh- Moisturp axe-5;; s sa as:

' Total tannazc...

ra as? In the above example the solution of oxaiicacid is added to ensure complete precipitation of the lignin in the lea'then In otherof-ymy-proc- 5 cases I may also add oxalic acid or otherqorgani'c --acids to facilitate the precipitation of the :lignin in. thehide. For instance, the precipitation of thelignin within the leather may belhastened a by the addition to the leather of acid substances such as fniter cakefoxalic acid, ,tartarieacid-pr .other uacid materials. Again, in applying -the,

, alkalinelignin solutions-to the leatherinstheextract wheel, that is, during. drumming, ,theex- 1' solution or sodium bisuitate or oxalic acidadded a'nd thereaiterythe wheel rotated ,for a .iurther period ot tocoinplete .the precipitation or ."the'il z it n wta ed s enl p er; .t ,7 v H tratesjthe ather:andcompletely preclpitates the ':Eidmple-'5;- ThiS CXB-HlDIQilllllStlfl-t;th-QIGD: 3 ar'ation '01 an 1 alkaline lignin solution fr'oni the" eeway, M1640 iruuy medmi fldq d v H thelmd r is thoroughly driven into vthe leather, about p :ininutes drumming-beingannually "flhen a assess Both. Usually' the1tannedfleathers are I v n completely precipilnordina per'ationsrvthis: vegetable. is

The so vextracting or drumming in w 35395. as" 3 scene:

g $5? am.

.'1l 1e1eath ers,obtained byany ot the foregoing proceduresshow ahighv degree of tannage, a high percentage: oi combinedtannin' and a low per- 1 centageoi' a-ewater gsqlubie, as .is evident i'rom -j-, the tables, giyea;ante.v Theso treated leathers Larealsdadyantagepus in that they are relatively gimperviousto changes sinv atmospheric or oilinatic conditions, such changes in humidity.

1Theprecipitatedflignin contained in the leather, isanonfhygroscopic and does not absorbmoisture. ;.'lhese LIignin-treated leathers also have a higher .pH -value and substantiaily v no mineral acidity or Procter-Searle value. 'lfhieisalso advantageoua. .Theexamplesjiyenante illustrate certain embodlments oi the present invention. In practising my invention tcthereembodiments thereoi" :may beemplcyedin commercial practice and in- -themgthe variousconditlons, such as the percentages, concentrations, time, temperature, etc., may

.be varied v according; to- 'the particular type of ucedf into the 'drum or extract mainstimates Thedrum, isthen'stppped' 01 1 1 5 9. 1%? fli 1 1 7 1 t n ;-rotated} i 'or ;an additional .20 minutes. 1; I ,7 J l -441 i?- e 'ifi j-theimnier'esedtina tanningsolution'ot "nanometer-twan I fit wrung bleached oiledanddrid.) I

j infg tab egiyeatheanaiysis-ofthe v 7 Leather alter L aiinc lignin alkaline ilgnin After 'this, temp e ring I such-as chestnut, quebracho, cutch, myrobalansj,

valonia, sumach, wattle, divi-divi, or other natural extracts; or with synthetic tannins such as aromatic sulphonic acids or sodium salts, or aromatic sulphonicacids partially or wholly condensed with .aldehydes or other similar .so-called synthetic tannins; or withmineral tanning" substances, suchas .basic chrome solutions or alum. Lignin additions are also usefulwith leather tanned with sulfite liquor preparations. In the examples 7 preparing the a alinelignin solutionsfrorn the dried or dehydrated lignin. This is advantageous, but it: is not absol tely necessary, to dry the wet precipitated lignin prior to forming such solutions, In some embodiments of, the present invention, I wash the precipitated lignin, and

"after filtering of! thewash liquors redissolve the wet precipitated lignin in alkaline solutions.

What I claim is: V. g 1. In the manufacture of leather, the improvement whichcomprises uimpregnating tanned leather'with recoveredlignin from woody fibers,

' solubilized by alkali, and insolubilizing the lignin in situ in the leather. a 2. The process 01 claim 1 wherein a slightly alkaline lignin solution is applied to a slightly acid tanned leather.

hide precipitates 3-. Asan improvement in tanning leather, the

process which comprises drumming tanned: hides ving a pH value in excess of 7 is prepared and this alkaline solution 0! recovthe alkalinity with a concentrated ered lignin .from woody fibers,

and concentration of said solution being so ad- M V vegetable tanned hide and carrying incorporated justed that the normal acidity of the tanned the lignin in insoluble form in situ in the hide.

4. In the manufacture of improvedleathers,

givenante, I havedescribed "cipitated lignin from ing the precipitatediignin and treating the lignin so obtained substantial amount.

the process which omprisesdrumming tanned hides withfla concentrated alkalinesolution oi recovered lignin from woody fibers, having a pH somewhat in excess of 7.0 until the alkaline lignin is absorbed bythe leather, adding *an acid solu- 'tionto the so impregnated leather and continuing the drumming until the lignin is precipitated upon the fiber in insoluble form. P 5, In the' manufacture of improved leather, the process which comprises dry dipping tanned leather in'a hot solution. of soluble alkalizcd recovered lignin irom woody fibers, having a pH value somewhat in excess 02-10;

6 The process or claim 5 wherein the said tannedleather contains su'fll'cient natural acids to precipitate the lignin on the fiber'in insoluble form. I I

7. Theprocess of claim 5 wherein thedrydipped"leatheris'subsequentlyimmersed in an acid solution to precipitate the absorbed lignin in insoiubleform.

8. Inthej manufacture of improved leathers, the improvement which comprises 3 the leather with a dry powdered alkaline lignin having a pH value in excess or 7.0. I

9.,In the'rnanuiacture of lignin preparations suitable for improving leather, the process which comprises acidifying black liquor with sufllcient acid to precipitate the-lignin, separating the prer the mother liquor, wash- 3,

I with sufllcient alkali soluble alkaline lignin.

10. The process of claim' 9 wherein a concen- I trated solution of said soluble alkaline lignin havto produce a lib solution applied to leather.

11;.- As a new material a leather made from recovered insoluble lignin from woody fibers, in do FREDRICK WALLACE. 

